Scintillation Flask Research Articles

Effective radium-226 concentration in rocks, soils, plants and bones

Abstract Effective radium-226 concentration, EC Ra , is the product of radium activity concentration, C Ra , multiplied by the emanation coefficient, E , which is probability of producing a radon-222 atom in the pore spaces. It is measured by accumulation experiments in the laboratory, achieved routinely for a sample mass >50 g using scintillation flasks to measure the radon concentration. We report on 3370 EC Ra values obtained from more than 11 800 such experiments. Rocks ( n =1351) have a mean EC Ra value of 1.9±0.1 Bq kg −1 (90% of data in the range 0.11–35 Bq kg −1 ), while soils ( n =1524) have a mean EC Ra value of 7.5±0.2 Bq kg −1 (90% of data between 1.4 and 28 Bq kg −1 ). Using this large dataset, we establish that the spatial structure of EC Ra is meaningful in geology or sedimentology. For plants ( n =85), EC Ra is generally <1 Bq kg −1 , but values of larger than 10 Bq kg −1 are also observed. Dedicated experiments were performed to measure emanation, E , in plants, and we obtained values of 0.86±0.04 compared with 0.24±0.04 for sands, which leads to estimates of the radium-226 soil-to-plant transfer ratio. For most measured animal bones ( n =26), EC Ra is >1 Bq kg −1 . Therefore, EC Ra appears essential for radon modelling, health hazard assessment and also in evaluating the transfer of radium-226 to the biosphere.

Effective radium concentration in agricultural versus forest topsoils

Effective radium-226 activity concentration (ECRa), the radon-222 source term, was measured in the laboratory with 724 topsoil samples collected over a ∼110 km2 area located ∼20 km south of Paris, France. More than 2100 radon accumulation experiments were performed, with radon concentration measured using scintillation flasks, leading to relative uncertainties on ECRa varying from 10% for ECRa = 2 Bq⋅kg−1 to less than 6% for ECRa > 5 Bq⋅kg−1. Small-scale dispersion, studied at one location with 12 samples, and systematically at 100 locations with three topsoils separated by 1 m, was of the order of 7%, demonstrating that a single soil sample is reasonably representative. Agricultural topsoils (n = 540) had an average (arithmetic) ECRa of 8.09 ± 0.11 Bq⋅kg−1, and a range from 2.80 ± 0.22 to 19.5 ± 1.1 Bq⋅kg−1, while forest topsoils (n = 184), with an average of 3.21 ± 0.14 Bq⋅kg−1 and a range from 0.45 ± 0.12 to 9.09 ± 0.55 Bq⋅kg−1, showed a clear systematic reduction of ECRa when compared with the closest agricultural soil sample. Large-scale organization of ECRa was impressive for agricultural topsoils, with homogeneous domains of several kilometers size, characterized by smooth variations smaller than 10%. These patches emerged despite heavy human remodeling; they are controlled by the main geographical units, but do not necessarily coincide with them. Valleys were characterized by larger dispersion and less organization. This study illustrates how biosphere and anthroposphere modify the soil distribution inherited from geological processes, an important baseline needed for the study of contaminated sites. Furthermore, the observed depletion of forest topsoils suggests an atmospheric radon signature of deforestation.

Optimized measurement of radium-226 concentration in liquid samples with radon-222 emanation

Measuring radium-226 concentration in liquid samples using radon-222 emanation remains competitive with techniques such as liquid scintillation, alpha or mass spectrometry. Indeed, we show that high-precision can be obtained without air circulation, using an optimal air to liquid volume ratio and moderate heating. Cost-effective and efficient measurement of radon concentration is achieved by scintillation flasks and sufficiently long counting times for signal and background. More than 400 such measurements were performed, including 39 dilution experiments, a successful blind measurement of six reference test solutions, and more than 110 repeated measurements. Under optimal conditions, uncertainties reach 5% for an activity concentration of 100 mBq L−1 and 10% for 10 mBq L−1. While the theoretical detection limit predicted by Monte Carlo simulation is around 3 mBq L−1, a conservative experimental estimate is rather 5 mBq L−1, corresponding to 0.14 fg g−1. The method was applied to 47 natural waters, 51 commercial waters, and 17 wine samples, illustrating that it could be an option for liquids that cannot be easily measured by other methods. Counting of scintillation flasks can be done in remote locations in absence of electricity supply, using a solar panel. Thus, this portable method, which has demonstrated sufficient accuracy for numerous natural liquids, could be useful in geological and environmental problems, with the additional benefit that it can be applied in isolated locations and in circumstances when samples cannot be transported.

Measuring effective radium concentration with large numbers of samples. Part I – experimental method and uncertainties

Effective radium concentration ECRa, product of radium concentration and radon emanation, is the source term for radon release into the pore space of rocks and the environment. To measure ECRa, we have conducted, over a period of three years, more than 5500 radon-222 accumulation experiments in the laboratory with scintillation flasks, and about 700 with integrating solid state nuclear track detectors, leading to experimental values of ECRa for more than 1570 rock and soil samples. Through detailed systematic checks and intercomparison between various repeated experiments, the experimental uncertainty has been assessed, and ranges from 30% (1 σ) for ECRa values smaller than 0.2 Bq kg−1 to about 8–10% for ECRa values larger than 50 Bq kg−1. The detection limit, defined as the 90% probability for obtaining a non-zero experimental ECRa value at 68% confidence level, depends on the mass of the sample with respect to the volume of the accumulation volume, and typically varies between 0.04 and 0.09 Bq kg−1. To measure ECRa from large numbers of samples with sufficient accuracy and uncertainty for our purpose, i.e. for the most natural objects encountered in the environment, the accumulation method with scintillation flask emerged as particularly useful and robust. Properties of ECRa and interpretations inferred from this large data set are presented in the companion paper.

Measuring effective radium concentration with large numbers of samples. Part II – general properties and representativity

Effective radium concentration ECRa, product of radium concentration and radon emanation, is the source term for radon release into the pore space of rocks and the environment. Over a period of three years, we performed more than 6000 radon-222 accumulation experiments in the laboratory with scintillation flasks and SSNTDs and we obtained experimental ECRa values from more than 1570 rock and soil samples. With this method, which allowed the measurement of ECRa from large numbers of samples with sufficient accuracy and uncertainty, as detailed in the companion paper, the dependence of the emanation factor on temperature and moisture content is revisited. In addition, with such a large ECRa dataset, dispersion of ECRa can be studied at sample-scale (cm to dm) and at scarp-scale (m to tens of m). Furthermore, we are able to discuss the representativity of obtained ECRa values at field-scale, and to investigate the spatial variations of ECRa over kilometric scales, within geological formations and across formations and faults. This experimental study opens new perspectives in the understanding of radium geochemistry and illustrates the importance of studying the radon source term with large numbers of samples for the modelling of geological and environmental processes, and also for the assessment of the radon health hazard.

Measuring effective radium concentration with less than 5 g of rock or soil

Radon generation in natural systems and building materials is controlled by the effective radium concentration ECRa, product of the radium concentration CRa and the emanation factor E. An experimental method is proposed to measure ECRa in the laboratory by radon accumulation experiments using less than 5 g of sample inserted in 125 mL scintillation flasks. Accumulation curves with fine temporal resolution can be obtained, allowing the simultaneous determination of the effective leakage rate. The detection limit, defined as the ECRa value giving a probability larger than 90% for a determination with a one-sigma uncertainty better than 50%, is moderate, varying from 2 to 5 Bq kg−1 depending on the conditions. Obtained punctual uncertainties on ECRa vary from about 10 to 20% at 10 Bq kg−1 to less than 3% for ECRa larger than 500 Bq kg−1. The representativity of small samples to estimate meaningful values at site or system level is, however, a definite limitation of the method, and the sample dispersion needs to be considered carefully in every case. Nevertheless, the value obtained with 5 g or less differs on average by 9 ± 13% from the value given by standard methods using 100 g or more, thus is sufficiently reliable for most applications. When ECRa is sufficiently large, the temperature sensitivity of ECRa can be measured reliably with this method, with obtained mean values ranging from 0.39 ± 0.05% °C−1 for Compreignac granite, to 2.8 ± 0.2% °C−1 for La Crouzille pitchblende, both from the centre of France. This method is useful to study dedicated problems, such as the small scale variability of ECRa, and in circumstances when only a small amount of sample is available, for example from remote areas or from precious materials such as historical building stones.

Heterogeneous temperature sensitivity of effective radium concentration from various rock and soil samples

Abstract. Temporal variations of radon concentration, or spatial variations around geothermal systems, are partly driven by the effect of temperature on the radon source term, the effective radium concentration (ECRa). ECRa from 12 crushed rock and 12 soil samples from Nepal was measured in the laboratory using the radon accumulation method and Lucas scintillation flasks at three temperatures: 7, 22 and 37 °C. For each sample and at each temperature, 5 or 6 measurements were carried out, representing a total of 360 measurements, with an ECRa average varying from 1.1 to 75 Bq kg−1. While the effect is small, ECRa was observed to increase with temperature in a significant and sufficiently reproducible manner. The increase was approximately linear with a slope (temperature sensitivity, TS) expressed in % °C−1. We observed a large heterogeneity of TS with average values (range min-max) of 0.79 ± 0.05 (0.16–2.0) % °C−1 and 0.61 ± 0.05 (0.10–2.0) % °C−1, for rock and soil samples, respectively. While this range overlaps with the results of previous studies, our values of TS tend to be smaller. The observed heterogeneity implies that the TS, rather poorly understood, needs to be assessed by dedicated experiments in every case where it is of consequence for the interpretation.

Radon emanation of heterogeneous basin deposits in Kathmandu Valley, Nepal

Effective radium-226 concentration ( EC Ra ) has been measured in soil samples from seven horizontal and vertical profiles of terrace scarps in the northern part of Kathmandu Valley, Nepal. The samples belong to the Thimi, Gokarna, and Tokha Formations, dated from 50 to 14 ky BP, and represent a diverse fluvio-deltaic sedimentary facies mainly consisting of gravelly to coarse sands, black, orange and brown clays. EC Ra was measured in the laboratory by radon-222 emanation. The samples ( n = 177) are placed in air-tight glass containers, from which, after an accumulation time varying from 3 to 18 days, the concentration of radon-222, radioactive decay product of radium-226 and radioactive gas with a half-life of 3.8 days, is measured using scintillation flasks. The EC Ra values from the seven different profiles of the terrace deposits vary from 0.4 to 43 Bq kg −1, with profile averages ranging from 12 ± 1 to 27 ± 2 Bq kg −1. The values have a remarkable consistency along a particular horizon of sediment layers, clearly demonstrating that these values can be used for long distance correlations of the sediment horizons. Widely separated sediment profiles, representing similar stratigraphic positions, exhibit consistent EC Ra values in corresponding stratigraphic sediment layers. EC Ra measurements therefore appear particularly useful for lithologic and stratigraphic discriminations. For comparison, EC Ra values of soils from different localities having various sources of origin were also obtained: 9.2 ± 0.4 Bq kg −1 in soils of Syabru–Bensi (Central Nepal), 23 ± 1 Bq kg −1 in red residual soils of the Bhattar-Trisuli Bazar terrace (North of Kathmandu), 17.1 ± 0.3 Bq kg −1 in red residual soils of terrace of Kalikasthan (North of Trisuli Bazar) and 10 ± 1 Bq kg −1 in red residual soils of a site near Nagarkot (East of Kathmandu). The knowledge of EC Ra values for these various soils is important for modelling radon exhalation at the ground surface, in particular in the vicinity of active faults. Importantly, the study also reveals that, above numerous sediments of Kathmandu Valley, radon concentration in dwellings can potentially exceed the level of 300 Bq m −3 for residential areas; a fact that should be seriously taken into account by the governmental and non-governmental agencies as well as building authorities.

Persistence of radon-222 flux during monsoon at a geothermal zone in Nepal

The Syabru-Bensi hydrothermal zone, Langtang region (Nepal), is characterized by high radon-222 and CO 2 discharge. Seasonal variations of gas fluxes were studied on a reference transect in a newly discovered gas discharge zone. Radon-222 and CO 2 fluxes were measured with the accumulation chamber technique, coupled with the scintillation flask method for radon. In the reference transect, fluxes reach exceptional mean values, as high as 8700 ± 1500 g m −2 d −1 for CO 2 and 3400 ± 100 × 10 −3 Bq m −2 s −1 for radon. Gases fluxes were measured in September 2007 during the monsoon and during the dry winter season, in December 2007 to January 2008 and in December 2008 to January 2009. Contrary to expectations, radon and its carrier gas fluxes were similar during both seasons. The integrated flux along this transect was approximately the same for radon, with a small increase of 11 ± 4% during the wet season, whereas it was reduced by 38 ± 5% during the monsoon for CO 2. In order to account for the persistence of the high gas emissions during monsoon, watering experiments have been performed at selected radon measurement points. After watering, radon flux decreased within 5 min by a factor of 2–7 depending on the point. Subsequently, it returned to its original value, firstly, by an initial partial recovery within 3–4 h, followed by a slow relaxation, lasting around 10 h and possibly superimposed by diurnal variations. Monsoon, in this part of the Himalayas, proceeds generally by brutal rainfall events separated by two- or three-day lapses. Thus, the recovery ability shown in the watering experiments accounts for the observed long-term persistence of gas discharge. This persistence is an important asset for long-term monitoring, for example to study possible temporal variations associated with stress accumulation and release.

Emanating power of 220Rn from a powdery radiation source

The emanating power (Fr) of 220Rn from a powdery sample was experimentally estimated. The powdery sample used in this study consisted of natural mineral encrustations left by a radioactive hot spring. The emanating power of thoron was analyzed based on both the theoretical emanation model of UNSCEAR and the result of the emanation test using the delayed-coincidence and time-analysis method with a flow-through scintillation flask. Finally, the maximum value of Fr for thoron was calculated to be approximately 0.5.

Time Variation of the Radon Equilibrium Factor in a Reinforced Concrete Dwelling

The time variation of the F value (equilibrium factor) was estimated for one year in a typical Japanese apartment of reinforced concrete using the following equipment: a 300 ml flow-through scintillation flask for the hourly variation of radon concentration and a WL meter for the equilibrium equivalent concentration of radon (EEC Rn). These monitors operated for four to eight days at the end of each month, and the information obtained was assumed to be the representative value for each month. The annual mean of F = 0.43 ± 0.09 found for the dwelling agrees very well with the UNSCEAR value of 0.4 for indoors. In addition, it appears that the monthly F value in the dwelling varies over the range by a factor of 3. In addition the tendency of the seasonal variation in the other countries located at middle geographical latitudes is also observed in Japan. The variation of the F value in this case is mainly based on the changes in the life styles and activities of the inhabitants, especially the ventilation condition of the room due to opening/shutting of windows and air-conditioner operation. In seasons when windows were shut, the F value increased: when the windows were open or the air-conditioners were on, the F value decreased, especially when the EEC Rn decreased as a result of the filtration effect. If it is necessary to determine the radon effective dose over a shorter period than one year, the time variation of each physical or environmental parameter including F value should be taken into account.

Continuous measurements of outdoor 222Rn concentrations for three years at one location in Colorado.

Measurements were made of 222Rn concentrations outdoors in Ft. Collins, Colorado, using a continuously sampling scintillation flask between January 1993 and December 1995. These data were analyzed for hourly, daily, and seasonal variations. The average 222Rn concentration at 1 m above the ground was 18 +/- 10 Bq m(-3) with a geometric mean of 15 Bq m(-3) and a geometric standard deviation of 1.7. Hourly averaged data indicated a diurnal pattern with the outdoor 222Rn concentration reaching a maximum in the early morning between 4:00 a.m. and 6:00 a.m. and a broad minimum between 1:00 p.m. and 4:00 p.m. in the afternoon. An analysis also indicated that the outdoor 222Rn concentrations were consistently lowest during the spring (March and April) and highest during the late summer (July-September).

Estimation Method for Alpha Particle Counting Efficiency for Scintillation Flasks

A simulation method to estimate counting efficiencies for 222 Rn and 220 Rn collected in a scintillation flask has been studied. The concept of this Monte Carlo calculation was based on a relationship between a residual range of an alpha particle colliding with a scintillator and an output-pulse-height distribution. The relationships were investigated using collimated beams of 241 Am because the pulse-height distributions differed not only with residual ranges but with distances between the collision point and the window of the flask. Using the distributions, counting probabilities for various alpha energies were estimated. The simulation for the counting efficiency was carried out using the following procedure: (1) a radiating point is determined by two random functions; (2) a radiating direction of an alpha particle is determined by other two random functions; (3) a counting probability for the alpha particle is calculated by the pulse-height distributions determined by the residual range at the collision point; and (4) the calculating cycle from (1) to (3) is repeated 100,000 times. The method was verified against experimental values for a standard 222 Rn gas and then adapted to 220 Rn. This method is very useful and effective because counting efficiencies of various scintillation flasks for various alpha particles can be estimated.

222Rn Emission Flux and Soil-Atmosphere Interface: Comparative Analysis of Different Measurement Techniques

Abstract Radon emission flux at the ground-atmosphere interface is one of the measurements commonly made for environmental purposes and on prospective mining sites. There are a number of ways of making such measurements. Generally an 'accumulation' technique is used. This method consists in determining the radon activity at a given time, inside a container placed on the ground with one side open, facing downward. The radon activity is determined by sampling the air inside the confinement system with a scintillation flask. The purpose of this work was to simplify this method by using other radon activity measurement techniques. The flux measurements made by the usual method, used as reference (spot sampling), were compared with those made using a silicon detector (continuous measurement) and with a solid trace detector (integrated measurement). For the latter two methods, a correction factor is applied to obtain the real value of the 222Rn emission flux yielded by the reference method.

Determination of Time-varying 222Rn Concentrations Using Flow-through Scintillation Flasks

This paper describes a method to obtain time-varying 222Rn concentrations from the series of gross alpha measurements recorded with a flow-through scintillation detector. The continuous input of 222Rn into the detector is treated as a series of independent pulses. The response of the detector to a single pulse containing 222Rn can be measured in the laboratory and is used to determine a normalized detector response function (NDRF). The NDRF contains information on the combined effects of detector design, operating parameters, and the presence of 222Rn progeny. The estimation of individual plate-out or counting efficiencies is not needed, as they are appropriately included in the NDRF. The equation describing the response function can be inverted to yield the actual 222Rn concentration in terms of detector output. The technique was applied to actual indoor monitoring data and the results presented.

Indoor Radon Measurements in the Shenzhen Region of the People's Republic of China

Indoor radon investigation has been conducted in the Shenzhen region, a coastal, subtropical city. Dual-filter, scintillation flask and activated carbon detectors were employed to study the regional distribution of 222Rn and its daughters in indoor air. By the end of 1986, measurements were made in 222 dwellings, including 147 high-rise buildings, 19 multi-family apartments, 50 detached houses and 6 basements. The average 222Rn concentrations in high-rise buildings, multi-family apartments, detached houses, basements and outdoors are 31.3, 15.5, 17.8, 108, and 13.7 Bq.m-3, respectively. The average alpha potential energy concentrations of 222Rn daughters in the above dwellings and outdoors are 1.58, 0.81, 1.02, 3.99 and 0.88 mWL, respectively. The equilibrium factors and indoor air exchange rates were also measured and are reported. Finally, the annual effective dose equivalents to the local residents have been estimated.

Measurement of the emanation of radon-222 from danish soils

The radon-222 emanation from 70 samples of Danish soils, subsoils, and sedimentary rocks has been measured. Two methods have been employed. The first one is to follow the growth of the radon concentration in a radon-tight sample container by transferring small air samples to a scintillation flask detection system. The second one is to measure the equilibrium gamma-activities of lead-214 and bismuth-214 in the sample when the sample container is open and, subsequently, when it is closed. Based on the measured emanation rates the samples are grouped in three classes: 1) less than 5 atoms · sec −1 · kg −1, 2) from 5 to 10 atoms · sec −1 · kg −1, and 3) more than 10 atoms·sec −1. In class 3) some diatomitic clays have shown emanation rates as large as 100 atoms·sec −1·kg −1.

A passive diffusion 222Rn sampler based on activated carbon adsorption.

A simple passive sampler for 222Rn with up to 24-hr integration times can be constructed by using a diffusion barrier to regulate the effective sampling rate of an ambient temperature activated carbon bed. The diffusion element serves to make sampler performance relatively independent of the properties of the type of carbon used. Satisfactory results are obtained if the total effective sample volume is kept well below the equivalent air volume of the activated carbon bed. The influence of various temperature and Rn profiles on the sampler's performance have been examined by experiment and by simulation. The amount of Rn adsorbed may be measured by gamma spectroscopy, by outgassing into an alpha scintillation flask, or by desorption into a liquid scintillator. In the latter case, a sensitivity of 0.2 pCi l-1 is obtainable for 24-hr exposures.

Liquid Helium Scintillation Counter as a Neutron Polarimeter

A liquid helium scintillation counter has been constructed and used in analyzing the spin polarization of neutrons in the range of energy near 20 Mev. Details of construction and operation of the device are described. The glass scintillation flask contains 8 moles of helium, and is supplied by a reservoir which provides 7 hours continuous operation under experimental conditions. The pulse-height spread for a source of natural alpha particles is approximately 25%. It is found that the attenuation of the helium scintillation light in the liquid is not appreciable at a distance of 10 cm, while the wavelength is observed to be less than 1600 A. Consequently, use of a fluorescent material as a wave shifter within the helium flask is required. The intensity of the wave shifted helium light compares favorably with that from CsI(Tl). The helium counter is used in coincidence operation with a plastic scintillator neutron detector. Under these circumstances, the width of a gated helium recoil pulse-height distribution is generally less than 30%. The geometry and electronics for a typical neutron polarization experiment are described.